Conventional silver halide photographic materials for colour prints have at least one yellow dye forming layer, at least one magenta dye forming layer and at least one cyan dye forming layer. After image wise exposure through a colour negative and subsequent processing in a colour developing process a colour print is obtained reproducing the colours of the originally photographed scene. Recently digital systems like Fuji's Frontier® system are used to produce such prints.
The extent to which the original colours can be reproduced is determined to a large degree by the choice of colour forming molecules or couplers and is referred to as the colour space of the set of couplers.
Conventional coupler sets are deficient in, reproducing neutral grey or black densities. Also deep colours such as shadow details in the original scene require high densities in the colour print in order to be reproduced naturally. conventional coupler sets have difficulty in reaching such high densities.
JP-B-83010737 describes a photographic material in which a low sensitive black dye forming layer using an aminophenol coupler is located under the other light sensitive layers to improve neutral grey densities.
JP-A-6395441 ads a black colour forming layer to a silver halide negative material to improve the overall sensitivity. The black colour forming layer contains a set of yellow magenta and cyan couplers or an aminophenol coupler.
JP-A-53133432 attempts to improve neutral and black densities by adding a black dye forming an aminophenol coupler into or adjacent to a silver halide emulsion layer. However, aminophenol black couplers have an inferior blue/black colour.
Photographic materials for black-and-white prints which can be processed in a colour developing process are described in, for example, JP-A10333296 and JP 05-232647. A black colour forming coupler is used. These comprise aminophenols and resorcinols. U.S. Pat. No. 5,821,039 describes the use of a 5-carbamoyl-resorcinol black coupler as an attempt obtain a black-and-white photographic material which has an improved black colour. Use of resorcinol couplers for colour photographic materials is not disclosed or suggested in these patents.
Although in the state of the art the importance of the stability of yellow, magenta and cyan dyes formed from their respective couplers has been recognized, and has been the subject of many improvements, the documents remain silent with respect to the stability of the dye formed from black couplers.